Jubilation about the German deal to save the euro could prove short-lived if fresh news of Greek tax evasion gains wider currency. There are more Porsche Cayennes registered in Greece than taxpayers declaring an income of 50,000 euros (£43,800) or more, according to research by Professor Herakles Polemarchakis, former head of the Greek prime minister’s economic department.

While German car workers may take pride in this evidence of their export success, German taxpayers may be less keen to bail out a nation whose population appears to take such a cavalier approach to paying its fiscal dues. Never mind all that macroeconomic talk about deficit distress, many Greeks are still plainly riding high on the hog.

Something can’t be right when the modest city of Larisa, capital of the agricultural region of Thessaly with 250,000 inhabitants, has more Porsches per head of the population than New York or London.

Perhaps the penny – or the euro – is already dropping, because Professor Polemarchakis writes that Larissa “is the talk of the town in Stuttgart, the cradle of the German automobile industry, and, particularly, in the Porsche headquarters there”, since it “tops the list, world-wide, for the per-capita ownership of Porsche Cayennes”.

“The proliferation of Porsche Cayennes is a curiosity, given that farming is not a flourishing sector in Greece, where agricultural output generates a mere 3.2pc of Gross National Product (GNP) in 2009 – down from 6.65pc in 2000 – and transfers and subsidies from the European Commission provide roughly half of the nation’s agricultural income.

“A couple of years ago, there were more Porsche Cayennes circulating in Greece than individuals who declared and paid taxes on an annual income of more than 50,000 euros.”

Hard to believe? Don’t take my word for it. The report in Athens News will add to fears, expressed by leading economist George Soros and others, that last week’s deal to save the euro can only buy a little time – not a permanent solution. China may also question why it should support economies that pay their unemployed more than most of its workers earn.

Binding such widely differing cultures as Greece and Germany together was always going to be a problem; not least because of diverging attitudes to such financial fundamentals as work and tax. Now, ahead of this week’s G20 Summit in Cannes, some euro-enthusiast must be sent to the cradle of culture to explain that deficits will balloon unless all taxpayers pay their fiscal dues. I nominate Vince Cable.